need help: dropbox files no longer availble on iPad

I use a web-based program called TherapyAppointment on my 10th gen 64 GB iPad which is running iOS 18.3.1. Until last night, I was able to attach small pdf files from dropbox to messages in TherapyAppointment. The process was seamless. Now, when I try to do this, I don't see dropbox at all.

The same holds true for accessing +/or saving dropbox files via the Highlights app, so the problem is not app-specific.

Nothing in my setup has changed recently. I've already contacted TherapyAppointment who they say nothing has changed on their end.

Any ideas on what happened about how to fix it? see pic: